Intracellular analysis of the development of responses of caudate neurons to stimulation of cortex, thalamus and substantia nigra in the kitten

Intracellular recordings were made from caudate neurons in anesthetized kittens of 2-72 days of age. In adult cats, results of intracellular recordings indicate that caudate neurons respond most frequently to stimulation of their major afferents from cortex, thalamus and substantia nigra with a sequence of excitation followed by inhibition (EPSP-IPSP sequence). The results of the present study show that the prominent IPSP of this sequence is not well developed in young kittens and does not reach adult values in terms of frequency of occurrence until beyond 40 days of age. Amplitude and duration of the IPSP evoked by cortical stimulation also did not reach adult values until beyond 40 days of age. In contrast, EPSPs can be evoked in the youngest kittens by stimulation of afferents to the caudate. These findings suggest that the caudate nucleus may alter its role during development. In early postnatal periods it functions as a simple relay system transmitting incoming information to its outputs in a relatively unaltered fashion. Later in development it becomes a system capable of complex modulation and filtering of neural information.